1. Field of the Invention
This invention relates to cyclic oligomers and a process for their preparation; the invention also relates to the use of the cyclic oligomers for the production of high molecular weight, linear polymers.
2. Description of Prior Art
High temperature polymers which are of high molecular. weight are difficult, if not impossible in many cases, to process in the melt because of their high melt viscosities at the elevated temperatures that would be required. Cyclic monomers and oligomers, since they are low molecular weight materials, have very low melt viscosities when heated which permits their fabrication into a desired shape whereafter they can be polymerized in situ to give the fabricated product.
Generally polymers of much higher molecular weight can be prepared from cyclics than in a conventional condensation polymerization reaction where the viscosity of the reaction mixture (solution or melt) limits the conversion in the polymerization reaction. Cyclic monomers and oligomers are thus potentially very important for the fabrication of advanced composites which contain large volume fractions of carbon fibers where precise alignment of the fibers is required to attain optimum properties, and for high performance adhesives since the cyclic materials can wet surfaces thoroughly and can then be polymerized in situ to give excellent bonding. Furthermore, the systems can often be designed so that the polymerized cyclic is crosslinked which offers further increases in temperature capability and also results in increased solvent resistance in the fabricated product.
A recent article ("Opening Rings to Polyethers" Chemtech, August, 1993, pp 25-28, by M. J. Mullins, E. P. Woo, D. J. Murray and M. T. Bishop) summarizes recent effects in the synthesis of cyclic oligomers of poly(aryl ether)s and methods to polymerize them with catalysts by a nucleophilic polymerization reaction.
Cyclic polycarbonate oligomers have been synthesized and it has been shown that they can be polymerized in situ to high molecular weight polycarbonates in the presence of a catalyst. (See U.S. Pat. Nos. 4,644,053; 4,696,998 and 4,727,134; also described in Polymer Preprints, American Chemical Society 30 (#2), 569, 571, 575, 577, 579, 581.) Mixtures of cyclics with linear polymers are obtained, which generally have to be separated, with yields of the cyclics being as high as 85%.
When spirobiindane bisphenols (SBI) are used higher yields of the cyclics are obtained so that often the cyclics can be used without separation of the linear polymer fraction. The rigid conformation of the SBI favors the formation of the cyclic. However, on polymerization residual amounts of the cyclics are retained because of the favorable ring-chain equilibrium (D. J. Brunelle, T. L. Evans and T. G. Shannon, U.S. Pat. No. 4,736,016, Apr. 5, 1988).
Cyclic poly(aryl ether) oligomers have also been synthesized in good yields along with the linear polymers (Mullins et al, above); (M. J. Mullins et al, U.S. Pat. No. 5,264,520; M. J. Mullins et al, U.S. Pat. No. 5,264,538). Using SBI as the bisphenol, cyclic poly(ether ketone)s and poly(ether sulfone)s have been synthesized in high yields. (J. M. Fukuyama, U.S. Pat. Nos. 4,959,454 and 5,110,893.)
Recently poly(ether ketone)s have been synthesized from the reaction of bisphenols with ortho-bis(4-fluoro- or 4-chlorobenzoyl)benzenes (A. S. Hay and R. Singh, U.S. Ser. No. 606,160, filed Oct. 31, 1990; R. Singh and A. S. Hay, Macromolecules 24, 2637-39 (1991); 24, 2640-42 (1991); 24, 2643-46 (1991)). These polymers are amorphous and have very high glass transition temperatures which increase with the number of pendant phenyl groups on the central benzene ring. The polymers can be converted to the corresponding phthalazines and isoquinolines by reaction with hydrazine and benzylamine, respectively. This conversion results in an increase in the solution viscosity as well as the glass transition temperature since the conversion results in a straightening of the chain and a resulting increase in the end-to-end distance as well as the rigidity of the polymer chain.